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From "Albert Lee (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (OPENJPA-2243) Deadlock involving FormatPreservingProperties
Date Fri, 27 Jul 2012 15:25:35 GMT

     [ https://issues.apache.org/jira/browse/OPENJPA-2243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Albert Lee updated OPENJPA-2243:
--------------------------------

    Patch Info: Patch Available
    
> Deadlock involving FormatPreservingProperties
> ---------------------------------------------
>
>                 Key: OPENJPA-2243
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-2243
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: lib
>    Affects Versions: 2.2.0
>         Environment: All environments
>            Reporter: Michael Pradel
>            Assignee: Albert Lee
>         Attachments: OPENJPA-2243.patch
>
>
> FormatPreservingProperties extends Properties, which is a thread-safe class, but it does
not preserve the thread safety. This leads to surprising deadlocks if you have a reference
of type Properties, because it may turn out to be not thread-safe (despite being documented
as such).
> Here's a simplified example that shows how we hit this bug:
> final Properties p1 = new Properties();
> final Properties p2 = createPropsWithDefault(p1);
> p2.put(p2, p2);
> 		
> Thread t1 = new Thread(new Runnable() {
>   public void run() { p2.remove(p1); }
> });
> Thread t2 = new Thread(new Runnable() {
>   public void run() { p2.stringPropertyNames(); }
> });
> t1.start();
> t2.start();
> try { t1.join(); t2.join();
> } catch (InterruptedException e) { e.printStackTrace(); }
> Properties createPropsWithDefault(Properties p) {
>   // return new Properties(p); // OK 
>   return new FormatPreservingProperties(p); // leads to deadlock
> }
> If createPropsWithDefault() returns Properties, everything is OK (as it should be, because
Properties is thread-safe). However, if it returns FormatPreservingProperties, we occasionally
get a deadlock.
> Are you aware of this inconsistency? It seems that the safest way of extending Properties
is to make methods that override synchronized methods synchronized.

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